<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div {
            width: 300px;
            background-color: rgba(0, 0, 0, 0.3);
            padding: 10px;
            position: relative;
        }
        input {
            border: none;
            padding: 10px 20px;
            width: 300px;
            box-sizing: border-box;

        }
        img {
            position: absolute;
            top: 14px;
            right: 30px;

        }
        p {
            font-size: 12px;
            color: red;
            margin: 0;
        }
    </style>
</head>
<body>
<div>
  <input type="text" placeholder="请输入用户名：">
  <img src="http://doc.canglaoshi.org/tstore_v1/images/login/yhm.png" alt="">
  <p>用户名不能为空！！</p>
</div>

</body>
</html>